Yeah I forgot that about berserkers, agreed.
Prodromoi: Skirmisher cavalry, with javelins and a short sword (Basically mounted peltasts) Not sure where they recruited from, though...
Hippeis: The noblemen of a polis who could afford a horse would join the citizen army on the back of their horses (unless they were Spartans) so they are very much like the Roman cavalry. But similar to the Romans, as we all know, the (poleis) Greeks weren't the greatest riders so they might rather be named Medium cavalry instead of Heavy cavalry (they barely stood a chance against Thessalian or Companion cavarly).
Hippokontistai (I guess you mean them? ) : Skirmisher cavalry like the Prodromoi from what I know. Not entirely sure here, but Prodromoi might be citizen cavalry while Hippokontistai might be mercenaries (others mods confirm the latter). Maybe Prodroimoi are poorer nobles or middle class men who had a horse and didn't want to fight as hoplites, while the hippokontistai were Northern Greeks (since Alexander also seems to have had some) who were hired as mercenaries by the poleis in urgent cases.
I'd say Hippokontistai should be made either mercenaries or more expensive both in upkeep and recruitment than the Prodromoi, but also stronger since mercenaries would have more experience in cavalry battles than, say, an Athenian trader.